They are used by the toys to communicate with each other, especially during the initial chaotic days at Sunnyside. The discs themselves are not explicitly shown, but their existence and use are implied throughout the movie.
Here are some clues:
* The use of picture-based communication: Early on, the toys at Sunnyside use drawings and gestures to communicate, suggesting a visual language system.
* The "pictomatic" reference: While not directly called "pictomatic discs," the toys refer to their communication system as something that "makes pictures," which implies a visual method of communication.
* The presence of a "pictomatic station": While not explicitly named, the toys use a central location with screens, hinting at a device for generating or displaying these images.
The film doesn't explicitly show the physical discs, but their presence is clear from the way the toys communicate.